the function of the small computer station along the rail behind the Captain/First Officer chairs? I don't recall it ever used before the arrival of Seven, but she seem to use it exclusively thereafter. Is it some kind of specialized Borg interface made just for her? Another sort of science station (which would make poor Harry even more useless)?

It's a generic "I'm on the Bridge" station. Neelix and the Doctor used it a few times too.